The present invention relates to a hydraulic control arrangement for automatically controlling the output shaft speed of an infinitely variable transmission, particularly for the operation of different auxiliary equipment.
In many cases it would be desirable to operate certain equipment at a constant speed while the speed of the power supply varies. Car engine accessories, in many cases, are needed to a greater degree when the car is moving slowly or at a standstill, that is, when the engine is idling, than at high vehicle and engine speeds. Power steering, for example, is hardly needed when a car is moving at high speeds on a straight highway but is utilized to its fullest during parking maneuvers. Demands on the air conditioning are much greater when a car is at a standstill or moving slowly, and the radiator fan is needed only during slow-speed operation of the vehicle since at travel speeds ram air alone is sufficient for radiator cooling. Also the alternator must be able to supply all the electric power required for the operation of the vehicle at engine idling speed.
All the accessories accordingly need to be oversized so as to be adequate at engine idle speeds. They are therefore generally relatively heavy and wasteful at higher speeds. They could be designed to substantially smaller sizes if they could only be operated at a predetermined design speed independently of the speed of their power supply. It may also be mentioned that a smaller engine would be sufficient to drive a particular vehicle. Smaller size equipment would not only be lighter and less expensive but it would also save a considerable amount of fuel.
Infinitely variable speed transmissions which could be used in connection with variable speed power supplies to provide a constant output speed for driving accessories are available but transmission controls are complicated, relatively unreliable and expensive.
Also a hydraulic speed control arrangement for such a transmission is known from Applicant's U.S. Pat. No. 4,501,172, which, in addition to controlling the speed of the transmission, provides for a supply of pressurized fluid for outside use, for example, for lubrication of bearings. However the amount of pressurized fluid needed for the operation of a particular accessory may vary substantially and flow variations would adversely affect the control since a constant size orifice determines the fluid flow and, as a result, the transmission ratio adjustment.
It would therefore be desirable to provide an inexpensive, simple and reliable speed control arrangement for an infinitely variable transmission with the aid of a hydraulic pump and control valve which would permit operation of engine accessories at a constant predetermined speed while deriving power from an engine operated at varying speeds and at the same time providing the appropriate amount of hydraulic fluid for driving some of the accessory equipment.